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51.
Urathamakul T Beck JL Sheil MM Aldrich-Wright JR Ralph SF 《Dalton transactions (Cambridge, England : 2003)》2004,(17):2683-2690
Electrospray ionisation mass spectrometry was used to investigate reactions between six ruthenium compounds and three different non self-complementary duplex oligonucleotides containing 16 base pairs. Each of the compounds studied formed non-covalent complexes containing between one and five ruthenium molecules bound to DNA. Competition experiments involving duplex 16mers and pairs of ruthenium compounds were used to determine the order of relative binding affinities of the metal compounds. Other competition experiments involving ruthenium compounds, and the organic DNA binding agents daunomycin and distamycin, provided information about the sites and modes of DNA binding of the ruthenium compounds. 相似文献
52.
Incorporation of a pyridine monomer into the backbone of a m-phenylene ethynylene oligomer allows functionalization of the interior binding cavity of the folded oligomer. The basicity of the inwardly directed pyridine moiety was modulated by changing the substituents on the pyridine ring and through oligomer folding, granting access to a pK(a) range of 5-14 in acetonitrile. [reaction: see text] 相似文献
53.
Brooks BC Meiere SH Friedman LA Carrig EH Gunnoe TB Harman WD 《Journal of the American Chemical Society》2001,123(15):3541-3550
The mechanisms for the interconversion of facial diastereomers of a variety of TpRe(CO)(L)(eta(2)-L(Ar)) complexes [L = (t)BuNC, pyridine (py), PMe(3), or 1-methylimidazole (MeIm); L(Ar) = benzene, anisole, naphthalene, 1-methylpyrrole, furan, or thiophene; Tp = hydridotris(pyrazolyl)borate] have been investigated by (1)H NMR spin saturation experiments. In addition, the rates and free energies of activation for these processes were calculated from spin saturation experiments and T(1) measurements. The operative mechanisms for interconversion of the pi diastereomers were found to be nondissociative, undergoing either an interfacial or intrafacial linkage isomerization. A comparison of the kinetic parameters for isomerization of related eta(2)-olefin complexes of the [TpRe(CO)(PMe(3))] and [CpRe(NO)(PPh(3))](+) fragments is also presented. 相似文献
54.
The extraction of the elements Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb and Bi into the solvents cyclohexanone, cyclohexanol, and cyclohexane from hydrochloric acid solutions, has been studied. Cyclohexanone is a more efficient but less selective extracting agent than cyclohexanol while cyclohexane has little extracting power. Solvent extraction of hydrochloric acid solutions of materials of geochemical interest into cyclohexanone has been used to enrich trace elements prior to spectrochemical analysis. 相似文献
55.
[reaction: see text] Glucuronyl iodide 1 has been studied in detail as a "disarmed" glycosyl donor. In a model reaction, using N-iodosuccinimide (NIS) as a promoter and 2-phenylethanol as acceptor, best results were obtained using NIS with I(2), followed by trimethylsilyltrifluoromethanesulfonate (TMSOTf). When a series of primary and secondary alcohols was glycosylated using these conditions, yields of 60-83% of beta-glucuronides were obtained. Various "nonheavy" metal salts also effectively catalyzed the model reaction but led to significant amounts of alpha-product with less reactive secondary alcohols. 相似文献
56.
Weronika Gruszka Anna Lykkeberg Gary S. Nichol Michael P. Shaver Antoine Buchard Jennifer A. Garden 《Chemical science》2020,11(43):11785
Heterometallic cooperativity is an emerging strategy to elevate polymerisation catalyst performance. Here, we report the first heterotrimetallic Na/Zn2 and K/Zn2 complexes supported by a ProPhenol ligand, which deliver “best of both” in cyclic ester ring-opening polymerisation, combining the outstanding activity (Na/K) and good control (Zn2) of homometallic analogues. Detailed NMR studies and density-functional theory calculations suggest that the Na/Zn2 and K/Zn2 complexes retain their heterometallic structures in the solution-state. To the best of our knowledge, the K/Zn2 analogue is the most active heterometallic catalyst reported for rac-lactide polymerisation (kobs = 1.7 × 10−2 s−1), giving activities five times faster than the Na/Zn2 complex. These versatile catalysts also display outstanding performance in ε-caprolatone and δ-valerolactone ring-opening polymerisation. These studies provide underpinning methodologies for future heterometallic polymerisation catalyst design, both in cyclic ester polymerisation and other ring-opening (co)polymerisation reactions.Cooperative heterotrimetallic Na/Zn2 and K/Zn2 complexes combine the excellent activities and control of the homometallic analogues, giving “best of both” in cyclic ester ring-opening polymerisation. 相似文献
57.
Bernard R. Brooks Duanka Janei
Martin Karplus 《Journal of computational chemistry》1995,16(12):1522-1542
Methods have been developed for the determination of vibrational frequencies and normal modes of large systems in the full conformational space (including all degrees of freedom) and in a reduced conformational space (reducing the number of degrees of freedom). The computational method, which includes Hessian generation and storage, full and iterative diagonalization techniques, and the refinement of the results, is presented. A method is given for the quasiharmonic analysis and the reduced basis quasiharmonic analysis. The underlying principle is that from the atomic fluctuations, an effective harmonic force field can be determined relative to the dynamic average structure. Normal mode analysis tools can be used to characterize quasiharmonic modes of vibration. These correspond to conventional normal modes except that anharmonic effects are included. Numerous techniques for the analyses of vibrational frequencies and normal modes are described. Criteria for the analysis of the similarity of low-frequency normal modes is presented. The approach to determining the natural frequencies and normal modes of vibration described here is general and applicable to any large system. © 1995 John Wiley & Sons, Inc. 1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America. 相似文献
58.
Jeffrey Axten Jennifer Troy Peter Jiang Mendel Trachtman Charles W. Bock 《Structural chemistry》1994,5(2):99-108
Ab initio molecular orbital calculations are used to study the modified Schlenk equilibrium: 2RMgCl (RMgCl)2 MgR2 + MgCl2 Mg(Cl2)MgR2 with R=H and CH3. In the absence of any solvents, calculations indicate that the formation of the various possible bridged dimers (RMgCl)2 is substantially exothermic. However, using dimethylether as a model solvent, we show that the formation of the dimer (Me2O)(CH3)Mg(Cl2)Mg(CH3)(OMe2) is exothermic only when entropic effects are included. 相似文献
59.
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